Post acceleration type cathode ray tube with perforated hollow collector electrode adjacent shadow mask

ABSTRACT

In a post acceleration type cathode ray tube of the class comprising a panel, a fluorescent screen coated on the inner surface of the panel, a funnel, an auxiliary electrode formed on the inner surface of the funnel, an electrode maintained at an intermediate potential and positioned to face the fluorescent screen for transmitting an electron beam, and a secondary electron collector electrode disposed close to the auxiliary electrode, the secondary electron collector electrode is constructed to transmit the secondary electrons generated by the other electrodes of the tube.

United States Patent 1191 Kasai Nov. 5, 1974 15 1 POST ACCELERATION TYPE CATHODE 2,230,134 1/1941 Colberg et a1. 313/85 R x RAY TUBE WITH PERFORATED HOLLOW Egg-" 34 3 1n COLLECTOR ELECTRODE ADJACENT 3,549,932 12/1970 Lindeman 313/85 S SHADOW MASK Inventor: Masayoshi Kasai, Mobara, Japan Assignee: Hitachi, Ltd., Tokyo, Japan Filed: Dec. 4, 1972 Appl. No.: 311,679

Foreign Application Priority Data Nov. 30, 1971 Japan .1 46-1l81l[U] US. Cl. 313/408, 313/450 Int. Cl H0lj 29/06, HOlj 31/20 Field of Search 313/85 S, 85 R References Cited UNITED STATES PATENTS 4/1936 Farnsworth 313/85 R X 1/1940 Epstein 3131/85 R X Primary Examiner-Robert Sega] Attorney, Agent, or Firm-Dike, Bronstein, Roberts, Cushman & Pfund [57] ABSTRACT In a post acceleration type cathode ray tube of the class comprising a panel, a fluorescent screen coated on the inner surface of the'panel, a funnel, an auxiliary electrode formed on the inner surface of the funnel, an electrode maintained at an intermediate potential and positioned to face the fluorescent screen for transmitting an electron beam, and a secondary electron collector electrode disposed close to the auxiliary electrode, the secondary electron collector electrode is constructed to transmit the secondary electrons generated by the other electrodes of the tube.

3 Claims, 4 Drawing Figures POST ACCELERATION TYPE CATHODE RAY TUBE WITH PERFORATED HOLLOW COLLECTOR ELECTRODE ADJACENT SHADOW MASK BACKGROUND OF THE INVENTION This invention relates to a post acceleration type cathode ray tube capable of efficiently collecting the secondary electrons generated in the tube. The well known post acceleration type cathode ray tube, a post acceleration type colour picture tube for example, schematically shown in FIG. 1, comprises a panel 1, a funnel 2 and a neck 3 which are sealed with each other to form an evacuated envelope. A fluorescent screen 4 is formed on the inner surface of the panel and a shadow mask electrode 5 supplied with an intermediate potential is mounted a predetermined distance apart from the fluorescent screen 4. The shadow mask electrode 5 is secured to the inner wall of the envelope by means of holders 6, generally in the form of leaf springs. An electron gun 7 is contained in the neck 3 and a funnel electrode 8 is applied on the inner surface of the funnel 2. A cylindrical inner shield electrode 9 having a construction shown in FIG. 2 is supported by the holders 6 in concentric relationship with the funnel electrode 8. A source of getter 10 is provided near the joint between the funnel and the neck.

The purpose of the inner shield electrode 9 is to prevent the getter material evaporated from the getter source 10 from depositing upon the fluorescent screen 4 and the shadow mask electrode 5 mounted on the panel thereby decreasing electric insulation strength between these members and thence causing unstable operation of the cathode ray tube and to accomplish the following object. Namely, in a post acceleration type colour picture tube, the speed of the electron beam passing through a passage between the electron gun 7 and the shadow mask electrode 5 is smaller than that of a colour picture tube not incorporated with the feature of post acceleration so that the electron beam is liable to be affected by magnetism or external magnetic field. The inner shield electrode 9 functions to eliminate such adverse affect of the magnetism or external field. Moreover, the inner shield electrode 9 functions to prevent a portion of the electron beam emanated from the electron gun from impinging upon the surface of the shadow mask electrode 5 that faces to the neck 3 thereby generating secondary electrons. A portion of such secondary electrons collides upon the funnel 2 to generate additional secondary electrons. These two types of secondary electrons impinge upon the fluorescent screen thereby causing undesired phosphor spots to luminesce thus decreasing the quality of the reproduced image.

In the conventional post acqeleration type colour picture tube, for the purpose of more efficiently preventing the generation of the secondary electrons, the surfaces of the shadow mask electrode 5, the inner shielding electrode 9 and the funnel electrode 8 are coated with a material that prevents the generation of the secondary electrons. Even with these various measures, secondary electrons are still generated thereby causing nonuniform luminescence and colour shading.

The above described problem of the secondary electrons of the post acceleration type colour picture tube also exists in the post acceleration type cathode ray tubes used for oscilloscope and the secondary electrons generated by the collector electrode cause the most serious problem.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide an improved post acceleration type colour picture tube utilizing an inner electrode of a novel construction that can effectively prevent the secondary electrons from impinging upon the fluorescent screen thereby preventing nonuniform luminescence and colour shadmg.

Another object of this invention is to provide an improved post acceleration type cathode ray tube used for oscilloscope and utilizing a collector electrode of a novel construction thereby preventing the secondary electrons generated by the collector electrode from impinging upon the fluorescent screen thus preventing deterioration of the picture quality.

Still another object of this invention is to provide a post acceleration type colour picture tube utilizing a perforated or mesh shaped inner shield electrode.

A further object of this invention is to provide an improved post acceleration type cathode ray tube used for oscilloscope which utilizes a perforated or wire mesh shaped collector electrode.

According to this invention, these and other objects are accomplished by providing a post acceleration type cathode ray tube of the class comprising a panel, a fluorescent screen coated on the inner surface of the panel, a funnel, an auxiliary electrode formed on the inner surface of the funnel, an electrode maintained at an intermediate potential and positioned to face the fluorescent screen for transmitting an electron beam, and a secondary electron electrode disposed close to the auxiliary electrode, characterized in that the secondary electron collector electrode is constructed to transmit trodes of the tube.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which FIG. I shows a diagrammatic longitudinal sectional view of a prior art post acceleration type colour picture tube;

FIG. 2 is a perspective view of the inner shield electrode shown in FIG. 1;

FIG. 3 is a perspective view of one example of the inner shield electrode utilized in the post acceleration type cathode ray tube of this invention and FIG. 4 shows a diagrammatic longitudinal sectional view of another embodiment of the novel post acceleration type cathode ray tube.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 3 of the accompanying drawing, there is shown an inner shield electrode 11 especially suitable for use in a post acceleration type colour picture tube. The inner shield electrode 11 has generally the same configuration as that shown in FIG. 2 but provided with a plurality of perforations I2.

With this improved construction, when secondary electrons are generated by the impingement of the electron beam upon the shadow mask electrode 5 for example, a portion of the secondary electrons is collected or absorbed by the inner shield electrode 11 and the remaining portion of the secondary electrons pass through perforations 12 to impinge upon the funnel electrode 8 and are absorbed thereby. Accordingly, the percentage of absorption of the secondary electrons which are generated by the shadow mask electrode 5 and other elements of the tube is much higher than that of the prior art post acceleration type cathode ray tube wherein the secondary electrons are absorbed by the inner shield electrode 11 and a substance coated thereon for absorbing secondary electrons.

Where the inner shield electrode 11 and the funnel electrode 8 are applied with the same potential and when the percentage of trasmission of the secondary electrons of the inner shield electrode 11 is denoted by I, and the yield of secondary electron of the inner shield electron 11 and the funnel electrode 8 by d and d respectively, then the apparent percentage of generation of the secondary electrons from these electrodes is given by an equation Assuming that the yield of secondary electron of respective electrodes are equal, that is d, d the percentage of generation of the secondary electrons would be minimum when 1 =0.5. Under these conditions the number of the secondary electrons generated will be decreased to about 25 percent of that the inner shield electrode of the conventional construction.

Where the potential of the funnel electrode 8 is higher than that of the inner shield electrode by about several tens volts, the inner shield electrode 11 acts as a suppression grid. Under these conditions, the percentage of the secondary electrons will be decreased to a low value which is nearly equal to (l -l)d,. Accordigly, under these conditions, it is advantageous to use a wire mesh shaped inner shield electrode having a high percentage of transmission of the secondary electrons.

FIG. 4 illustrates a modified embodiment of the post acceleration type cathode ray tube which is especially suitable for oscilloscope in which the same or corresponding elements to those shown in FIG. 1 are designated by the same reference numerals. In this modified embodiment, there are provided a cylindrical perforated collector electrode 15, a mesh electrode 16 mounted on the collector electrode 16 at one end thereof facing the fluorescent screen 14 and a helical electrode 17 applied on the inner surface of the funnel, these electrodes corresponding to the inner shield electrode, the shadow mask electrode and the funnel electrode, respectively of the previous embodiment. Like the inner shield electrode 11 shown in H6. 3, the collector electrode 15 is provided with a plurality of perforations. Alternatively, the collector electrode may take the form of a wire mesh with this construction the secondary electrons generated are absorbed by the cooperation of the collector electrode 15 and the helical electrode 17 at extremely higher efficiencies than the prior art cathode ray tube.

Although, it is preferred to provide the performations for transmitting the secondary electrons over the entire surface of the secondary electron collector electrode, substantially the same object can also be accomplished by providing such perforations only at the portions of the collector electrode close to the electrode at the intermediate potential.

Although the invention has been shown and described in terms of some preferred embodiments thereof, it should be understood that many changes and modifications will be obvious to one skilled in the art within the scope of the invention as defined in the appended claims.

What is claimed is:

1. In a post acceleration type cathode raytube of the class comprising a panel, a fluorescent screen coated on the inner surface of said panel, a funnel, an auxiliary electrode coated on the inner surface of said funnel, a neck, at least one electron gun positioned within said neck, said panel, funnel and neckcooperating to form a sealed envelope, an electrode having perforations for transmitting an electron beam maintained at a potential below the post acceleration potential and positioned in front of said fluorescent screen, and a hollow secondary electron collector electrode positioned within the envelope and having open ends, said collector electrode forming an enclosure surrounding the path of the electron beam directed toward the fluorescent screen from the electron gun, the improvement in which said secondary electron collector electrode is constructed to have perforations for transmitting a portion of the secondary electrons generated by other electrodes of said tube to said auxiliary electrode.

2. The cathode ray tube according to claim 1 wherein said perforations are provided over the entire surface of said secondary electron collector electrode.

3. The cathode ray tube according to claim 1 wherein said inner shield electrode comprises a wire mesh electrode. 

1. In a post acceleration type cathode ray tube of the class comprising a panel, a fluorescent screen coated on the inner surface of said panel, a funnel, an auxiliary electrode coated on the inner surface of said funnel, a neck, at least one electron gun positioned within said neck, said panel, funnel and neck cooperating to form a sealed envelope, an electrode having perforations for transmitting an electron beam maintained at a potential below the post acceleration potential and positioned in front of said fluorescent screen, and a hollow secondary electron collector electrode positioned within the envelope and having open ends, said collector electrode forming an enclosure surrounding the path of the electron beam directed toward the fluorescent screen from the electron gun, the improvement in which said secondary electron collector electrode is constructed to have perforations for transmitting a portion of the secondary electrons generated by other electrodes of said tube to said auxiliary electrode.
 2. The cathode ray tube according to claim 1 wherein said perforations are provided over the entire surface of said secondary electron collector electrode.
 3. The cathode ray tube according to claim 1 wherein said inner shield electrode comprises a wire mesh electrode. 